Lawyers in the case say roadblocks -- a widely used law enforcement tool -- may have broader legal implications in the war on terror.

At issue is whether police using a roadblock to investigate one felony can arrest a stopped person for a separate, unrelated crime. Vehicle stops without specific, prior suspicion of wrongdoing have traditionally been declared unconstitutional under the Fourth Amendment's ban against "unreasonable searches and seizures."

The case concerns a hit-and-run-investigation by the Lombard Police Department, a Chicago, Illinois, suburb. A 70-year-old man had been struck on his bicycle by a car in August 1997. Investigators a week later set up a checkpoint at the same hour and location, handing out fliers and asking drivers for information. Police contend the stops lasted about 10-15 seconds each, and say drivers were not asked for their names, drivers license, or any personal information.

Then along came Robert Lidster. Police claim his car nearly struck officers and that his breath smelled of alcohol. He was ordered to pull over, and after undergoing sobriety tests, was arrested and charged with driving under the influence.

Lidster claims he passed the sobriety tests, and that the roadblock was an illegal invasion, since the public interest in setting up a checkpoint did not outweigh the intrusion on his rights as an innocent motorist.

The Illinois Supreme Court eventually agreed. In its ruling, the court concluded, "The right of an individual to be free from unreasonable searches and seizures is an indispensable freedom, not a mere luxury." State officials then appealed to the Supreme Court.

'Why is it different if it's a car'
In arguments Wednesday, the justices seemed especially curious about exactly when police should be allowed to use roadblocks and for what purpose.

"Is it often roadblocks are set up to get information" about a past crime, Justice Sandra Day O'Connor asked Illinois Solicitor General Gary Feinerman, who defended the practice .

"Is it permissible to cordon off sidewalks, where pedestrians are funneled through a chute" for questioning, followed Justice David Souter.

Justice Antonin Scalia seized on that, saying "Why is it different if it's a car?"

Chief Justice William Rehnquist took things a step further, quizzing whether officers could block roads and ask motorists for donations to a police charity. Lidster's attorney, Donald Ramsell, said that might be permissible under the law, since a crime was not involved. That was the opening Rehnquist was looking for. "So you can hold up a bunch of people for 10 minutes for money, but you can't hold them up for 10 to 15 seconds to ask for information about a crime?"

Other justices offered a variety of scenarios, asking whether roadblocks could be used to investigate child abductions, rape-murders, and serial killers, serious crimes that may have been committed within the hour and perhaps weeks earlier.

Case may have implications for war on terror
Legal experts say this type of questioning may be signal the justices are laying the legal groundwork for potentially similar scenarios involving the fight against terrorism.

"This is the one case so far that is clearly about 9/11," said David Yalof, a political scientist at the University of Connecticut, and author of "Pursuit of Justices." "Law enforcement is telling the courts that in a post-9/11 world the rules have changed. They want more latitude to set up roadblocks, things like that, to prevent terrorism and other violent crimes. And it's unclear how the Supreme Court will respond to that kind of argument."

Many defense attorneys and civil rights groups fear the government could use checkpoints as an excuse to conduct sweeping dragnets on the broader community, targeting certain ethnic, religious, or minority groups in hopes of catching criminals.

"The Constitution simply does not allow the police to stop and detain individuals in order to determine what information they might have about some criminal activity by another individual or individuals," said Harvey Grossman, legal director for the ACLU of Illinois, which filed its own brief supporting Lidster. "If this type of roadblock were permissible, the fundamental protection of the Fourth Amendment -- to preserve our personal autonomy from government intrusion -- would be irrevocably undermined."

Ramsell said roadblocks should rarely be used "unless, for example, there is an imminent terrorist attack. But he said that in this case there was "no evidence this roadblock would advance the interest to solve the crime," in the face of reasonable alternatives, which he said could include door-to-door canvassing of homes and businesses and a media campaign.

"Motorists have the right to be left alone and the right of free passage," he argued

But Illinois' top lawyer, Feinerman, said that with informational roadblocks, "you're just being asked to help" solve a crime, and that drivers need not fear police intrusion, calling public cooperation "an act of responsible citizenship."

Courts in general have upheld the use of roadblocks, but only in narrow instances, such as border and sobriety checkpoints, and emergencies such as the 2002 search for the Washington-area sniper suspects.

The Supreme Court three years ago, in the case known as City of Indianapolis v. Edmond, ruled police checkpoints of vehicles in Indianapolis to look for illegal drugs was improper.

Illinois is supported by 14 other states that filed a supporting legal brief with the court. These states argue for continued use of roadblocks. "The need for officers to feel they can take action reasonably calculated to advance a pending investigation -- possesses enhanced significance in an age where our nation seeks to protect itself not only against the traditional threat of conventional crime, but against international terrorism as well."